A silver (Ag) metal has optical properties sensitive to a size and shape thereof, and indicates high plasmon excitation efficiency, high electric conductivity, and high thermal conductivity. It was found that an Ag nano-particle using these properties is a prominent material in a field such as an organic catalyst field, an optical sensor field, an electronic printing field, a photonics field, and the like.
Since a size and shape of this Ag nano-particle have a large influence on optical, electrical, and surface energy properties, it is important to synthesize significantly uniform Ag nano-particle. In order to synthesize the Ag nano-particle by a bottom-up method, basically, an experimental environment capable of reducing Ag+ ions in a solution containing the Ag+ ions should be prepared.
Introducing synthesizing methods of an Ag nano-particle, a method of transferring UV/vis energy, microwave energy, or ultrasound energy to a solution via radiation to reduce Ag+ ions, a method of adding a strong reducing agent such as borohydride based reducing agents, hydrazine, or the like, at room temperature, and a method of adding a weak reducing agent such as sodium citrate, ascorbic acid, or polyol in a state in which a solution is heated, have been known.
Among the methods as described above, in the energy radiation method, a synthetic method is significantly simple, but it is impossible to apply uniform energy to the entire reaction solution, such that non-uniform particles are generated. In addition, in the method of adding an arbitrary reducing agent, since various chemical species such as a surfactant, a solvent, a reducing agent in addition to an Ag precursor are added, synthetic cost is increased, such that this method is not suitable for mass-production.
Therefore, in a preparing method for mass-producing an Ag nano-particle in an industrial field, the chemical species should be minimally required in synthesis, the cost should be cheap, an amount of energy applied thereto should be small, and the Ag nano-particle should be prepared through a simple processing step.